Electromagnetic devices, such as transformers and reactors, are used in power systems for voltage level control. Hereto, a transformer is an electromagnetic device used to step up and step down voltage in electric power systems in order to generate, transmit and utilize electrical power in a cost effective manner. In a more generic sense a transformer has two main parts, a magnetic circuit, the core, made of e.g. laminated iron and an electrical circuit, windings, usually made of aluminium or copper wire.
Larger transformers used in electrical power networks are generally designed with high efficiency and with a set of stringent operational criteria, e.g. dielectric, thermal, mechanical and acoustic criteria. Due to continuously increasing power handling capacity, i.e. power and voltage rating of transformers, transformer designs face more and more constraints.
Modern practices of transformer design involve inter alia balancing the use of materials in the core and winding, and losses. Due to the large amount of power handled by a large power transformer and due to long service life, typically 40 years, any improvement in reduction of losses would be appreciable, if it can be justified by the cost.
Power Loss in transformers due to load currents is a large part of the total losses. The load loss (LL) consists of perceivably three different types of losses based on their origin, i) the I2R losses due to inherent resistance of winding conductors, also called DC loss, ii) the eddy current loss (ECL) in the windings due to the time-varying magnetic field created by the load current in all winding conductors, the leakage field and iii) the stray losses, i.e. ECL in other structural parts of the transformer due to the leakage field.
Current solutions for reducing eddy current losses include multi-strand continuously transposed cables (CTC). These cables require stronger copper in order to be able to handle short circuits in high voltage applications. Moreover, the manufacturing of CTC cables having a plurality of sufficiently thin and transposed strands is a very expensive process and requires gluing and insulation of the strands by means of epoxy. The material cost of high voltage inductive devices hence increases tremendously.